Radio receiving system



Jan. 1, 1929. 1,697,042

R. BOWN RADIO RECEIVING SYSTEM Filed Aug. 19, 1924 IN VEN TOR PatentedJan. 1,- 1929.

UNITED STATES RALPH IBOWN, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TOAMERICAN TELEPHONE` 1,697,042 PATENT oFFicE.

AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

RADIO mncniviive ySYSTEM.

, Application led August 19, 1924. Serial No. "732,968.l

This invention relates to radio receiving systems, and particularly tovisual indicating means to insure the proper adjustment of the tuningcircuits inorder lto effect the best reception.

In highly selective radio receiving sets, it is difiicult to tune suchsets exactly without using an indicating instrument in the plate circuitof a detector tube to determine when the carrier frequency of theincoming` signal coincides with the resonant frequency of the circuit.rlhis method, however, is not applicable to receiving` sets of thedouble detection type having intermediatefrequency amplification` andemploying a band-pass filter for selectivity.

It is the object of this invention to provide means for insuring theproper tuning of receiving sets having a band filter or its equivalentconnected therewith.

This invention will be clearly understood from thev followingdescription, when read in connection with the attached drawing, showingschematically a form of embodiment of the invention.

n the drawing, the antenna 1 is coupled by the transformer 2 with theinput circuit of the detector 3. The input circuit is tuned by means ofthe winding 4 and condenser 5 for the band of frequencies desired to bereceived. Also connected with this input circuit by means of thetransformer 6 is a source 7 of oscillations to beat down the incomingoscillations to provide an intermediate frequency. rfhis intermediatefrequency will be impressed upon the amplifier 8, the output side ofwhich is connected with the band-pass filter 9. Oscillations passingthis filter are impressed upon the low frequency detector 10, the platecircuit of which includes the condenser 11 and the inductance 12.Bridged across the said inductance is a, vacuum tube 13 having in itsplate circuit an indicating instrument 14, which together constituteavacuum tube voltmeter. The constants ofthe condenser 11 and theinductancelQ are so chosen that the plate circuit will be resonant tothe mid-frequency of the band passed by the filter 9 and the vacuum tubevoltmeter will indicate the condition of resonance. Bridged across theplate circuit of the detector 10 in parallel with the said resonantcircuit and the voltmeter is an audio-frequency circuit which isconnected with the receiver 16 by means of the transformer 15; i

Having in. mind the description of the apparatus which'makes up thecircuit, the invention will now be clear from the following descriptionof the methbd of tuning the circuit in order to effect proper receptionof signals. Let it be assumed that the incom- 4 ing signal is made up ofa carrier frequency ofl7 50,000 cycles, with two side bands of 5,000cycles eac-h. That is to say, the incoming frequencies may berepresented by a band eX- tending fro-in 745,000 to 755,000-cycles.Since the circ-uit 4--5 is tuned for this band, the potentials thereofwill be impressed upon the grid circuit of the detector 3, together withoscillations from the source 7. As a result of the beating operation, anintermediate band ofv frequencies will be produced, which will beamplified by 8 and impressed upon the f band-pass filter 9, which isdesigned to pass a band extending from 40,000 to 50,000 cycles. ln orderthat the resultant band may pass through this filter, the source 7 ofthe beating oscillations must be operated at 705,000 or 7 95,000 cycles.The frequency representing the midpoint of the band passed by the filter9 is that for which the circuit 11-12 is resonant. In other words, ifthe oscillator 7 is properly adjusted, such condition will be indicatedby the visual indicating instrunient 14, which shows the condition ofresonance of the current fiowing through the circuit 11-1-12. It willtherefore be'noted thatthe band of frequencies resulting from beatingthe incoming frequencies with the oscillations from the source 7 will beproperly i centered upon the bandpa`ss filter 9, and therefore, themaximum result will be obtained in the receiving apparatus 16 con-'nected with the audio-frequency circuit.

consequently, the indicating device would4 not need to heqiiarticularly'sensitive.

`While this invention has been disclosed as embodied in a particularform and arrangenient of parts, it is not so limited but is capable ofembodiment in other forms without departing from the spirit and scopo ofthe appended claims.

lV hat is .claimed is:

l. In a radio receiving system, the combination with a vacuum tubedetector, the plate circuit of which is tuned to a known frequency, of abandpass filter designed to pass a band of frequencies, the midpoint ofwhich is the frequency at which the said plate cir.- cuit is resonant, avisual indicating device connected With the plate circuit to show theexistence of resonance, and a source of received oscillations and asource of beating oscillations connected with the input side of saidfilter to produce the said bandof frequencies transmitted thereby.

2. In a radio receiving system, the combination with an antenna of adetector having a source of beating oscillations connected therewith, abandpass filter designed to pass the difference frequency, between theincoming frequency and the beating frequency, a second detector havingritsplate circuit tuned to the 4niid-frequency of the band passed by thesaid filter, and means to indicate the potential acrossthe said tunedplate circuit,

3. In an alternating current signaling system the combination with avacuum tube detector of a sourcel of oscillations to produce a hand offrequencies, a filter connected between the said source and the saiddetector designed to pass the said 'frequency band, a selecting networkconnected with the output circuit of the .said detector adjusted to passan undetected component of the output of the said detector, nectcd withthe said selecting network.

4. In an alternating current. signaling system the combination with avacuum tube detect-or of a source of oscillations toproduce a band offrequencies, a filter connected bctween the said source and the saiddetector designed to pass the said frequency band, a selectingnetworkconnected with the output circuit of the said detector adjusted to passthe mid-frequency of the said band, and an indicating device connectedwith the selec"- ing network.

In testimony whereof, I havesigned my name to this specification this18th day of August 1924.v

RALPH BOWN.

and an indicating device conf

